Small areas of surgical destruction (lesions) in the anterior limb of the internal capsule of the brain (anterior capsulotomy) have proved helpful for many patients who remain disabled with Obsessive Compulsive Disorder (OCD) in spite of conventional therapies. Lesions in a different brain location, the nucleus ventralis intermedius of the thalamus, have proved beneficial for tremors (uncontrollable shaking) which do not respond to medication. For tremors, chronic electrical simulation through electrodes implanted in the thalamus (deep brain stimulation, or DBS) has proved as effective as lesions, making it unnecessary to destroy brain tissue. This suggests that chronic stimulation through electrodes in the anterior limb of the internal capsule might substitute for anterior capsulotomy in the treatment of OCD. We now propose a pilot study to investigate whether this may be the case. If so, chronic electrical stimulation would be preferable for a number of reasons. We also propose to use scanning by positron emission tomography (PET) with [18F] fluorodeoxyglucose (FDG) to determine which areas of the brain are activated by electrical stimulation in this portion of the internal capsule. This will provide basic information on brain connections and function and may provide clues to the brain mechanisms of OCD. Subjects will be five patients with OCD refractory to conventional therapies, who would otherwise be candidates for anterior capsulotomy. After diagnostic and baseline studies, electrodes will be placed in the anterior limbs of each internal capsule by precise stereotactic technique and connected to electrical pulse generators implanted under the skin. After surgery the DBS system will be tested in-hospital to assess for side effects and complications, to identify possible immediate therapeutic effects, and to search for optimum stimulation settings. Subsequently, as outpatients, each patient will undergo periods of several weeks each, in which stimulation will alternately be turned on and off in a double blind design in order to verify any apparent benefits and to test for possible benefits of prolonged stimulation. Symptom severity and impairment scores will be assessed during each period. At the completion of the study, patients will be given the choice of continued stimulation, anterior capsulotomy, or further conventional therapy.